1. Field of the Invention
The invention pertains to medical body temperature control blankets of the pneumatic disposable type wherein an envelope defined by synthetic plastic sheets is pressurized by a temperature regulated air and the air is ejected upon the patient through the blanket lower sheet.
2. Description of the Related Art
A common treatment for post-surgery trauma, hypothermia and other life threatening temperature related trauma is to place a body temperature control blanket over the patient and impinge air upon the patient's body at a desired temperature to endeavor to raise, or lower, the temperature of the body. Usually, the patient is treated with heated air, but it is also possible to use blankets of this type to distribute cool air over the patient. Such thermal blankets take a variety of forms, and a lightweight disposable version of the general type of the instant invention is shown in the assignee's U.S. Pat. Nos. 5,125,238 and 5,246,656, and the purpose and advantages of this type of blanket are set forth in these patents.
A disposable temperature controlling blanket is usually formed of synthetic thermoplastic sheets, such as of a vinyl material which are heat sealed at their periphery to define a blanket. Openings located within the lower sheet permit the pressurized air within the blanket as supplied through an inlet port to be distributed over the patient's body. Usually, the upper and lower sheets will be welded or tacked at spaced locations to control the extent of envelope inflation, as will be appreciated from the disclosure of U.S. Pat. No. 5,125,238.
For a variety of reasons, it is desirable to locate the blanket pressurized air inlet port at the blanket lower end, with respect to the patient's head, and accordingly, heated air introduced into the blanket lower end tends to cool as the air travels the length of the blanket due to the fact that the blanket sheets are directly exposed to the ambient air. Such cooling of the temperature control air introduced into the blanket envelope prevents an even temperature of air from being distributed over the patient's entire body, and the even distribution of air temperature within the blanket envelope is a serious problem.
Patents for improving the distribution of substantially equal temperature air throughout the blanket is shown in the assignee's U.S. Pat. No. 5,265,599 entitled Patient Temperature Control Blanket With Controlled Air Distribution, and Ser. No. 08/078,842, now U.S. Pat. No. 5,304,217. In these disclosures, an enlarged air passage is defined within the central region of the envelope in communication with the pressurized air inlet as defined by closely spaced weldments or tacking wherein the upper and lower envelope sheets are heat sealed together. The forming of such a central air flow passage encourages the air entering the central region of the envelope to travel the length of the envelope before being laterally disbursed into the other blanket regions. This approach to achieving a more uniform distribution of the air temperature within the blanket envelope is generally successful, but because the upper and lower envelope sheets are exposed to ambient air, heat loss still occurs from the blanket central region as the air therein travels lengthwise through the blanket.